1. Field of the Invention
The present invention relates generally to electrochemical cells. More specifically, the present invention relates to an improved dual porosity electrode for use in electrochemical systems wherein simultaneous transport of gas and liquid into and/or out of the electrode is required.
2. Description of the Related Art
U.S. Pat. No. 4,738,904, issued Apr. 19, 1988, and assigned to the present assignee, discloses a thermoelectrochemical system in which a continuous electrical current is generated from heat input below 250.degree. C. In this system, a hydrogen ion reacting cathode is immersed in a chosen Bronsted acid and a hydrogen ion reacting anode is immersed in a chosen Bronsted base. Reactants consumed at the electrodes during the electrochemical reactions are directly regenerated thermally below about 250.degree. C. and recycled to the electrodes to provide continuous operation of the system. The electrodes used in this type of thermoelectrochemical system are typically composed of platinum or other catalytic particles which are held together by a support network of microscopic hydrophobic fibers made from materials such as polytetrafluoroethylene (PTFE).
In operation of the above thermoelectrochemical system, hydrogen gas reacts with ammonia or an amine vapor in microscopic pores in the anode electrode to generate an electron and an ammonium ion or a protonated amine. The protonated amine ion is transported through a membrane in the cell to the cathode. The protonated amine is transported into the microscopic pores of the cathode which are present between the platinum particles. Within these microscopic pores, a liquid acid and an electron react to produce hydrogen gas and an acid anion. The anion combines with the protonated amine ion to form a liquid salt. For the cathode to operate effectively, fresh acid must enter the electrode structure while simultaneously allowing the hydrogen gas and the salt to escape from the structure. Accordingly, it would be desirable to provide an electrode which is designed to allow simultaneous transport of gas and liquid into and/or out of the electrode in an efficient manner to improve performance of thermoelectrochemical systems of the type described in the above-mentioned patent.